Efficient enablement for wireless communication on license-exempt bands

ABSTRACT

A fixed or Mode II device enables a Mode I device for license exempt operation by providing to it a list of available license exempt radio channels and a parameter indicating an interval at which contact verification signals CVSs are to be sent. The CVSs verify whether the list remains valid. The fixed/Mode II device then repeatedly sends contact verification signals spaced in time from one another according to the interval. In various embodiments the parameter may be an explicit indication (number of seconds or number of beacons between consecutive CVSs), or it may be implicit (derived from an ID of the fixed/Mode II or Mode I device or a frequency channel, in which the relevant ID is the parameter). A plurality of enabled Mode I devices each gets a device-specific list, and in one embodiment the interval is the same for each of them and the explicit indication is broadcast while in another the parameter is provided to each of them via unicast messages and the interval may differ.

CROSS REFERENCE TO RELATED APPLICATION

Subject matter detailed herein is related to that detailed at co-ownedU.S. patent application Ser. No. 13/184,702, filed on Jul. 18, 2011 andentitled ‘Wireless Network Operation on License-Exempt Band”. Thatrelated application is herein incorporated in its entirety.

TECHNICAL FIELD

The exemplary and non-limiting embodiments of this invention relategenerally to wireless communication systems, methods, devices andcomputer programs and, more specifically, relate to techniques andprocedures for keeping devices enabled for communication over availablelicense-exempt channels.

BACKGROUND

The following abbreviations that may be found in the specificationand/or the drawing figures are defined as follows:

CVS contact verification signal

DA destination address

E-UTRAN evolved UMTS terrestrial radio access network

FCC Federal Communications Commission

IBSS independent basic service set

ID identifier

IEEE Institute for Electrical and Electronics Engineers

MAC medium access control

RX receive

SA sender address

SSID service set identifier

TVBD television band device

TVWS television white spaces

TX transmit

WLAN wireless local area network

To alleviate congestion in conventional cellular spectrum, research hasturned recently to exploiting license-exempt radio spectrum such as theindustrial, scientific and medical (ISM) band and what in the UnitedStates are known as TVWS, which is a particular portion of thelicense-exempt spectrum which was at one time set aside for televisionbroadcast but which in recent years has become increasingly availablefor other radio communications. In general license-exempt radio spectrumis sometimes referred to as a shared band, contrasted with conventionalcellular systems which utilize radio spectrum for which the systemoperator holds a license from a government regulator such as the FCC inthe United States. Administration of wireless operations on suchlicense-exempt bands is quite country-specific at least at this earlystage, with the FCC implementing regulations for use of the TVWS in theUnited States.

In the United States it is envisioned that there will be whitespace orTV band databases indicating, for specific geographic areas orgeo-locations, which portions of that license-exempt spectrum areavailable to parties other than those involved with televisionbroadcasting. Such portions may be identified in the relevant databaseas indexed channels, bandwidth and center frequency, upper and lowerfrequency bounds, or other frequency-definitive parameters.

Relevant to TVWS in the United States, the FCC defines two concepts foraiding users in finding available channels; a TV bands database assummarized above and the geo-location capability. See for exampledocument FCC 10-174; SECOND MEMORANDUM OPINION AND ORDER; UNLICENSEDOPERATION IN THE TV BROADCAST BANDS—ADDITIONAL SPECTRUM FOR UNLICENSEDDEVICES BELOW 900 MHZ AND IN THE 3 GHZ BAND (adopted and released Sep.23, 2010). The TV band database is to maintain records of all authorizedservices in the TV frequency bands and so is capable of determining theavailable channels as a specific geographic location. Such available (orequivalently the used) channels are provided as lists to TVBSs that havebeen certified under the FCC's equipment authorization procedures. Someof the TVBDs will have a geo-location capability, and those devicesshould be able to determine their own geographic coordinates within acertain level of accuracy (+/−50 m). This capability is used with a TVbands database to determine the availability of TV channels at a TVBD'sgeo-location. The FCC defines several types of TVBDs as follows based onthose devices' characteristics.

A fixed TVBD is located at a specified fixed location and has thefollowing functions/capabilities: it can select a channel from the TVbands database; it can initiate and operate a network (by sendingenabling signals to other fixed TVBDs and/or personal/portable TVBDs);and it can provide to a Mode I personal/portable device (see below) alist of available channels on which the Mode I device may operate(currently, above TV channel 20) and a supplemental list of availablechannels for Mode I devices (these available channels are adjacent tooccupied TV channels and are those on which a fixed TVBD cannotoperate). Examples of what may operate as a fixed TVBD in the LTE systeminclude an access node/eNodeB, a mobility management entity MME, aserving gateway S-GW, a local gateway L-GW, and a packet gateway P-GW.Similarly functioning nodes in other radio access networks may alsoserve the functions of a fixed TVBD. The maximum power a fixed TVBD isallowed to deliver to its TX antenna shall not exceed 1 W, and themaximum power spectral density (any 100 kHz during any time interval ofcontinuous transmission) is 12.2 dBm.

A Mode I personal/portable device is another of the FCC's TVBD types.This type does not use any internal geo-location capability it may have(if any) to find its TVWS channels so even if it can access a TV bandsdatabase the mode I device must obtain its channel list from either afixed TVBD or from a Mode II personal/portable TVBD (see below). A ModeI device may operate only as a client or dependent station/device, butnot as an enabling station/device.

A Mode II personal/portable device is a portable device having similarfunctions as a fixed TVBD, but does not need to transmit/receive signalsat a specified and fixed place. For personal/portable TVBDs, the maximumeffective isotropic radiated power (EIRP) is 100 mW (20 dBm). If thepersonal/portable TVBD does not meet the adjacent channel separationrequirements (the distance between the TVBD and the TV station issmaller than the minimum distance requirement), the maximum EIRP is setto 40 mW (16 dBm). The maximum power spectral densities forpersonal/portable devices operating adjacent to occupied TV channels is−1.6 dBm, otherwise 2.2 dBm.

And finally the FCC has designated a sensing only device, which is apersonal/portable TVBD that uses spectrum sensing to determine a list ofavailable channels. It can use the frequency bands 512-608 MHz (TVchannels 21-36) and 614-698 MHz (TV channels 38-51). Currently, the FCCdefines spectrum sensing only for personal/portable TVBDs. The maximumpower spectral density for sensing only devices is −0.8 dBm.

The IEEE 802.11 af standard being drafted (D1.02; June 2011) is intendedto amend the 802.11 specification for TVWS operation by, among otheraspects, fulfilling the above requirements. The document FCC 10-174cited above further requires that Mode I devices are to be enabled by a(fixed or) Mode II device (called enabling station), and then onceenabled the Mode I device may start transmission on an availabletelevision channel or channels (more generally, a TVWS frequencyresource).

A problem arises in the procedure for enabling a Mode I device. Havingfirst obtained the list of available TVWS channels, the Mode I devicemust receive a CVS at least every 60 seconds to verify its list. Such asCVS signal is shown at reference number 412 of FIG. 4 in theabove-referenced co-owned U.S. patent application Ser. No. 13/184,702.At §15.71 of the above referenced document FCC 10-174 the CVS is definedas follows:

-   -   “(b) Contact verification signal. An encoded signal broadcast by        a fixed or Mode II device for reception by Mode I devices to        which the fixed or Mode II device has provided a list of        available channels for operation. Such signal is for the purpose        of establishing that the Mode I device is still within the        reception range of the fixed or Mode II device for purposes of        validating the list of available channels used by the Mode I        device and shall be encoded to ensure that the signal originates        from the device that provided the list of available channels. A        Mode I device may respond only to a contact verification signal        from the fixed or Mode II device that provided the list of        available channels on which it operates. A fixed or Mode II        device shall provide the information needed by a Mode I device        to decode the contact verification signal at the same time it        provides the list of available channels.”

In practice the transmission interval of the CVS signal should be morefrequent, because in case there is only one CVS transmission during a 60second period a mode I device which misses it would have to stopoperation on TVWS and get re-enabled before it can transmit again. Or ifthe 60 second time limit is approaching the Mode I can request CVSenablement from the Mode II device which originally provided the list,in which case the Mode II device does not have to track the 60 secondtimer for every device which it has enabled.

The FCC regulations provide that the Mode II device which provided thechannel list for a Mode I device is also required to transmit CVSsignaling to each of its enabled devices. But a given Mode II device mayenable several Mode I devices on several different channels, and hereinlies the problem which is illustrated by example at FIG. 1.

There is a Mode II AP 24 which enables communication on severalchannels, shown by example as starting from channel #20 (Ch20) up tochannel #N (Ch#N). The enablement may be non-contiguous meaning thatcertain channels between Ch20 and Ch#N will not be available at thisparticular location. By enabling multiple STAs 20, 22, 23 andpotentially also APs (mode I APs) 21 on different channels, on differentparts of spectrum, the enablement signaling load of Mode II APincreases. For multiple Mode I devices enabled by a single Mode IIdevice, this is too high of a burden to the enabling device 24 whichmust frequently re-check the TVWS database and redistribute the channellist. The conventional procedure is also seen to be too high a burden onthe enabled Mode I devices 20-23.

Apart from the documents FCC 10-174 and IEEE 802.11af noted above, alsorelevant to these teachings are:

-   -   document IEEE 802.11-11/908r1 entitled “Secure Enablement and        CVS without Persistent Association”, by Qualcomm (Jul. 5, 2011);    -   Section 8.3 of IEEE Draft P802.11-REVmb™/D8.01 (May 2011)        concerning frame type formats; and    -   3GPP TS 36.331 V10.2.0 (2011-06) (Release 10).

SUMMARY

In a first exemplary embodiment of the invention there is an apparatuscomprising at least one processor and at least one memory storing acomputer program. In this embodiment the at least one memory with thecomputer program is configured with the at least one processor to causethe apparatus to at least: enable a device for operation in a licenseexempt spectrum by providing to the device a list of available licenseexempt radio channels; provide to the device a parameter indicating aninterval at which contact verification signals are to be sent, in whichthe contact verification signals verify whether the list remains validand repeatedly send contact verification signals spaced in time from oneanother according to the interval.

In a second exemplary embodiment of the invention there is a methodcomprising: enabling a device for operation in a license exempt spectrumby providing to the device a list of available license exempt radiochannels; providing to the device a parameter indicating an interval atwhich contact verification signals are to be sent, in which the contactverification signals verify whether the list remains valid; andrepeatedly sending contact verification signals spaced in time from oneanother according to the interval.

In a third exemplary embodiment of the invention there is a computerreadable memory storing a computer program, in which the computerprogram comprises: code for enabling a device for operation in a licenseexempt spectrum by providing to the device a list of available licenseexempt radio channels; code for providing to the device a parameterindicating an interval at which contact verification signals are to besent, in which the contact verification signals verify whether the listremains valid; and code for repeatedly sending contact verificationsignals spaced in time from one another according to the interval.

In a fourth exemplary embodiment of the invention there is an apparatuscomprising at least one processor and at least one memory storing acomputer program. In this embodiment the at least one memory with thecomputer program is configured with the at least one processor to causethe apparatus to at least: receive from an enabling device a list ofavailable license exempt radio channels; and determine an interval, froma parameter received from the enabling device, at which contactverification signals are spaced in time from one another, in which thecontact verification signals verify whether the received list remainsvalid.

In a fifth exemplary embodiment of the invention there is a methodcomprising: receiving from an enabling device a list of availablelicense exempt radio channels; and determining an interval, from aparameter received from the enabling device, at which contactverification signals are spaced in time from one another, in which thecontact verification signals verify whether the received list remainsvalid.

In a sixth exemplary embodiment of the invention there is a computerreadable memory storing a computer program, in which the computerprogram comprises: code for receiving from an enabling device a list ofavailable license exempt radio channels; and code for determining aninterval, from a parameter received from the enabling device, at whichcontact verification signals are spaced in time from one another, inwhich the contact verification signals verify whether the received listremains valid.

These and other embodiments and aspects are detailed below withparticularity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of a single Mode II device enabling four ModeI devices on different TVWS channels, and illustrates an environment inwhich embodiments of the invention may be practiced to advantage.

FIG. 2 is a schematic diagram showing the frame structure of aconventional management frame in an IEEE 802.11af radio access system.

FIG. 3 is a schematic diagram showing the conventional structure of ageneric variable length information element disposed in the frame bodyof the FIG. 2 management frame which may be adapted to include the CVSinformation detailed herein.

FIG. 4 is a conventional system information block in an E-UTRAN/LTEsystem which may be extended according to these teachings to include theCVS information detailed herein.

FIG. 5 is a logic flow diagram that illustrates the operation of amethod, and a result of execution of computer program instructionsembodied on a computer readable memory, from the perspective of theenabling device 24 of FIG. 1 in accordance with the exemplaryembodiments of this invention.

FIG. 6 is a logic flow diagram that illustrates the operation of amethod, and a result of execution of computer program instructionsembodied on a computer readable memory, from the perspective of anenabled device 20-23 of FIG. 1 in accordance with the exemplaryembodiments of this invention.

FIG. 7 is a simplified block diagram of various devices shown at FIG. 1,which are exemplary electronic devices suitable for use in practicingthe exemplary embodiments of the invention.

DETAILED DESCRIPTION

While the exemplary embodiments detailed below are in the context ofWLAN and other similar ad hoc networks, these teachings apply also toother structured radio access technologies such as for example globalsystem for mobile communication (GSM), universal terrestrial radioaccess network (UTRAN), evolved UTRAN (E-UTRAN), and their futureevolutions. Since the terminology for the various devices may be countryspecific, the FCC Mode II device is more generally termed an enablingdevice and an FCC fixed device may also operate as an enabling device;the FCC Mode I device is more generally termed an enabled device; andthe TVWS is more generally referred to as license exempt bands orchannels.

First consider the scenario by which the first enabled device 20 of FIG.1 becomes enabled by the enabling device 24 (though the same applies toany of the enabled devices 20-23). In the WLAN or ad hoc context theenabled devices 20-23 are operating as (non-access point) stations STAand the enabling device is operating as an access point AP. It isnotable that the different enabled devices 20-23 may be enabled fordifferent license exempt channels as shown at FIG. 1; having them allenabled for the same license-exempt channel is likely to result ininterference or undue delay when they all compete for resources usingsome contention procedure.

After authentication and association the first enabled device 20receives encryption keys for the CVS reception from the enabling device24. The first enabled device 20 will not stay associated since it mayhave no data but wishes to remain enabled. Some reasons it may wish toremain enabled despite having no data to send is to operate on theunlicensed band (for example, set up an IBSS network), or to connect toan access point which is also a mode I device (such as the Mode I device21 which is a WLAN AP for other WLAN devices/stations 20, 22 in itscoverage area and which is enabled by the enabling device 24) area), orto setup communications quickly after going into a sleep mode.

According to an exemplary embodiment of these teachings, the enablingdevice transmits an indication of the CVS transmission periodicity. Thisindication of the CVS interval may be broadcast in the enabling device'sbeacon message, or it may be transmitted in a management frame such asfor example an action frame or in the enabling device's broadcast systeminformation. Depending on the type of management frame they may bebroadcasted or uncasted. In one embodiment the CVS interval is the samefor all of the enabled devices, and this embodiment is most easilyimplemented if the parameter indicating the CVS interval is broadcast;in another embodiment the CVS interval is different for at least two ofthe enabled devices (or at least the CVS interval is not necessarily thesame for them all), and this embodiment is most easily implemented ifthe parameter indicating the CVS interval is sent to the enabled devicesvia individual unicast messages. In various implementations this CVSinterval may be expressed as a clock measurement such as a number ofmilliseconds, or as a system frame measurement such as a number ofbeacons between CVS transmissions. So while the enabling device 24 canenable the various enabled devices 20-23 on multiple and/or differentlicense exempt channels, the enabling device 24 needs to transmit theCVS interval indication on only one channel and that indicated CVSinterval is valid for all the channels which the enabling device 24 hasincluded in the Available Channel List which the enabling device 24 mostrecently provided to all its various enabled devices 20-23. For the casein which there is a single CVS interval for all of the devices, it isvalid for all the channels which the enabling device 24 has included inthe all of the Available Channel Lists which it provided to the variousplurality of enabled devices 20-23.

In one exemplary embodiment, the enabling device 24 also indicates thespecific channel or channels on which it will send the CVS transmissionor transmissions. That is, the CVS transmission may configure a specificone (or more) of the enabled devices 20-23 for a specific channel onwhich that enabled device(s) is to receive its CVS transmission. Even ifthere are multiple CVS transmissions to different devices on differentchannels, all such CVS transmissions from the enabling device 24 followthe CVS interval which is indicated on one channel that all the devicescan access. So any given device 20-23 which desires to become or toremain enabled, but has no immediate need to transmit its own data, canread the CVS interval indication from the enabling device's 24 beacon(or system information or other management/action frame) and go into areduced power/sleep mode for a relatively extended period of time. Inthis manner the enabled devices 20-23 are able to forego checking everybeacon from the enabling device 24 and need not be awake for every CVStransmission from the enabling device 24.

A Mode I device 20-23 which is enabled by a Mode II device 24 may obtainthe CVS interval from the Mode II device 24 and, in one non-limitingembodiment, may further repeat the Mode II CVS interval information(parameter) in its own broadcast transmission. This is especially usefulfor the case of an ad hoc network in which the Mode II device 24 setsthe same CVS interval for all of its enabled devices 20-23. But in thiscase the Mode I device repeating the CVS interval information does notre-send the content of the CVS message itself, only the parameterindicating the CVS interval.

The various implementations of the indicated CVS interval mentionedabove (number of milliseconds, number of beacons) imply an explicitindication. In other exemplary embodiments the indication can beimplicit. For example, the CVS interval may be derived by the variousinvolved devices 20-24 utilizing the device ID given by thenetwork/enabling device 24. In one implementation of this the CVStransmission may be an encrypted broadcast message, and the CVS intervalmay be derived by applying a function to the access point/enablingdevice ID and the frequency channel ID. In this case it is efficient forthe enabling device 24 to make the CVS interval identical for all of theenabled devices 20-23. In another implementation the CVS transmission isan encrypted unicast message and the CVS interval is derived from thereceiving device ID (e.g., the ID of the enabled device 20-23 addressedby the unicast message). If encrypted broadcasting is not supported bythe network (which is the case presently with WLAN systems) thisembodiment can be used, where the network would then use dedicatedsignaling to get the encrypted CVS messages to the individual enableddevices 20-23 and the CVS interval is not necessarily identical for allof those enabled devices 20-23 (though if for example a modulo operationis used on the device ID it may be that some but not all enabled devicesget identical CVS intervals). In a still further implementation the CVStransmission interval is derived from any combination of the accesspoint ID, the device ID, and the frequency channel ID. Such a device IDmay be implemented as a temporary one assigned by the network, such asan association ID for WLAN networks, radio network temporary ID (RNTI)in LTE, and other such network assigned identifiers in other radioaccess technologies.

The above explicit and implicit implementations can be generalized asthe enabling device 24 repeatedly sending CVSs, spaced in time from oneanother, according to a single interval, in which that interval isindicated by a parameter the enabling device 24 sends to each of theenabled devices 20-23. For the explicit indication the parameter is thatexplicit indication, which as above may indicate a number of seconds ora number of beacons between consecutive ones of the repeated CVSs. In amost general sense, it is the network/enabling device 24 whichconfigures the CVS interval, as opposed to the conventional FCC rulenoted in the background section above which simply mandates a CVS bereceived by the enabled devices at least once every 60 seconds.

For the implicit indication the parameter may be one or any combinationof an identifier an individual one of the plurality of the enableddevices 20-23, an identifier the enabling device 24, and/or anidentifier of a frequency channel. These parameters are then insertedinto some predetermined function (such as for example a modulo functionon the whole identifier or on certain predetermined most or leastsignificant bits thereof) known in advance to both the enabling device24 and the enabled devices 20-23 (such as may be published in a wirelessprotocol/standard and locally stored at the various devices 20-24) toderive the interval. For the case of the enabled device ID this is sentin a unicast message; for the case of the enabling device ID this issent in its system information or possibly also in its beacon; for thecase of the frequency channel ID this may be the ID of the channel onwhich the beacon is sent (and so communicated to the enabled devices20-23 in system information for example). As another example of thefrequency channel ID, the relevant channel may be that over which theCVS signal itself is provided by the Mode II device 24. IN the WLANsystem the channels are identified by index numbers, other non-WLANimplementations can use a similar channel index number or otheridentifier number assigned by the network. Or the network may insteaduse an ID obtained from combining two or more individual TVWS channels.

In the various implementations above, or any which use an encryptedmessage for the CVS signal, it is preferable that the encryption bechanged from time to time so as to retain its security features. To thisend the enabling device 24 provides a new encryption key each time itchanges the encryption, and the enabling device 24 provides each newencryption key with the current CVS signal itself just before making thechange.

For the above aspects of these embodiments in which there is a change tothe encryption key, the key change can be triggered periodically by theenabling device 24 which tracks this via a timer (either a single timerif the CVS interval is the same for all enabled devices 20-23 ormultiple timers if there are multiple different CVS intervals runningconcurrently); if the key has not been changed when the timer expiresthen expiry of the timer will cause the enabling device 24 to change theencryption. Any time the key is changed, in an embodiment the enablingdevice 24 will send the current CVS signal with the new key multipletimes to better assure the affected enabled device or devices 20-23 areable to obtain it. Just in case any do not, then an enabled device 20-23which did not obtain the new key can utilize the CVS request procedure(which was noted above in the context of its 60-second CVS timer nearingexpiry) to obtain the new encryption key by utilizing the old encryptionkey. In this case the network/enabling device 24 can configure avalidity time for the old key, and the old key used with such a CVSrequest procedure will be valid to obtain the new key only through theend of that validity time.

In an exemplary embodiment, anytime the enabling device 24 needs toupdate any enabled device's available channel list, the enabling device24 will begin the key change procedure. But in other embodiments the keychange may be up to the enabling device's discretion, and if a new keyis only recently adopted when a channel list update occurs the enablingdevice 24 may choose not to re-issue a new encryption key.

The encryption keys may be specific per enabled device 20-23. Forexample, if there is a specific channel list update request triggered byan individual enabled device 20-23 and that request is sent to a fixedenabling device, that fixed enabling device may begin the key changeprocedure for only that requesting enabled device, or may perform thekey update procedure for all of the enabled devices which are using thatsame channel list which is being updated. In this context the specificchannel list refers to a channel list that is only allowable for modeI/II devices, the license exempt available channel list which the modeII device gets from the TVWS database.

For added security in the key change procedure, the signaling to triggerthe CVS key change can provide a new sequence which is not a decryptionkey in and of itself for the new encryption the enabling device 24 isabout to use, but which is used together with the old key to derive theactual new decryption key. This derivation can also be a function knownto the various devices 20-24 in advance, such as may be published in awireless protocol/standard and locally stored in their respectivememories. This implementation prevents the new decryption key from beingsent over the air interface. Any of the enabled devices 20-23 can getthe initial decryption key from the enabling device 24 at the time theyobtain their initial channel list.

Since the above provisions for various exemplary embodiments have thenetwork/enabling device 24 configuring the CVS interval rather thanusing some fixed value (e.g., 60 seconds) which applies regardless ofwhich enabling device and traffic conditions, then the network/enablingdevice can in certain exemplary embodiments also configure the relevanttimers in the enabled devices 20-23. These include the timer whichtriggers a given enabled device 20-23 to send a request for a CVS, whichfor convenience is denoted as T_(CVRC). The enabled devices 20-23 mayneed to send a CVS request for example if their decoding (or evendecrypting) of the CVS fails and they do not wish to wait an additionalinterval to see if their allowed channel list is still valid.

By example, the network/enabling device 24 may take considerations oftraffic and connectivity requirements of the current service intoaccount when configuring the T_(CVRC) for the enabled devices, and/ormay scale this timer with the amount of enabled devices 20-23 that areassociated with (enabled by) the enabling device 24. For implementationsin which the CVS message is not broadcast by the enabling device 24 (forexample, where encryption of broadcast messages is not supported by thesystem), the enabling device 24 may send the CVSs as unicast frames andset the interval a bit longer than if broadcasting were available, butgiven the FCC rule detailed in background above such longer intervalshould still be less than 60 seconds. In any case, the T_(CVRC) whichthe network/enabling device 24 configures for the enabled devices 20-23should be greater than the CVS interval it configures and also less than60 seconds.

For those embodiments in which the CVS is sent in a broadcast message,that same broadcast message may additionally carry information about theavailable channel list. If the channel list is changed the enablingdevice 24 will need to inform the enabled devices 20-23 that the channellist has changed, and in this embodiment can inform them also in thatsame CVS broadcast message. Once the list of available channels doeschange, the enabling device 24 will then broadcast the new channel listto the enabled devices 20-23 with the same encryption key but themessage includes a new key (or new sequence used to derive the new key)which is used for the next encrypted broadcast with the CVS. If the CVStransmission is a broadcast message, the enabled devices 20-23 shouldnot make unicast channel requests to the enabling device 24.

FIG. 2 gives an example of a conventional MAC layer management frameunder the 802.11 protocol which can be readily adapted with newinformation elements to implement the above embodiments concerningbroadcasting the CVS signals. While FIGS. 2-3 are in the context of WLANframes, similar implementations for other radio access technologies arereadily adapted from these WLAN examples.

The 802.11 specifications provide for three basic frame types: controlframes, data frames, and management frames. Management frames include,among others, beacon frames, public action frames, and action frames.Management frames have fixed headers and information is carried in theframe body in discrete information elements. FIG. 2 illustrates amanagement frame divided broadly into the frame header 202 and the framebody 216 which carries the information elements.

The header is divided into discrete fields. There is a frame controlfield 204 which indicates for example the protocol version and frametype (and possibly also frame subtype). There is a duration field 206which indicates a duration value of the frame, how long it is. There isa DA field 208 which carries the destination MAC address and a SA field210 which carries the sender MAC address. The header 202 also defines aBSS ID field 212 which carries the basic service set ID for the senderand a sequence control field 214 which contains values for the recipientto check for duplicate frames.

The frame body 216 carries the information elements and certain otherfixed fields. Following the frame body 216 is a frame check sequencefield 218 that carries a cyclic redundancy checksum of the whole frame.The frame body 216 consists of fixed length fields and variable lengthinformation element fields.

FIG. 3 illustrates a generic format for one information element field;there is an identifier field 302 to identify the particular informationelement, a length field 304 to indicate how long is the informationelement, and an information component 306 which carries the relevantinformation for that information element and whose size is governed bythe length field 304. In WLAN-specific embodiments of these teachingsthere may be an information element for the CVS, and which also includesthe indication of the CVS interval for those implementations where thatindication is explicit.

FIG. 4 gives an example of a System Information Block (SIB) Type 1message, conventional for the E-UTRAN/LTE radio access technology, andtaken from 3GPP 36.331 v 10.2.0 (2011-06). This conventional systeminformation block (or master information block MIB) may be readilyadapted/extended to implement the above embodiments concerningbroadcasting the CVS related information. FIG. 4 is a non-limitingexample; other types of system information blocks can be used toimplement this aspect of the invention or a new system information blockmay be developed to do so. If not broadcast, for the E-UTRAN/LTE systemthe network/enabling device 24 can configure the UE specific parametersvia dedicated radio resource control signaling.

For such a E-UTRAN/LTE implementation, there may additionally besignaling among the higher network node/mobility management entity (MME)and the eNodeB/enabling device 24 and the enabled devices 20-23 so as toimplement the CVSs and the CVS interval indications detailed more fullyabove. For example, each logical entity could be defined to manage itsown CVS related encryption keys, and this entity shall interact with theMME and possibly also the home subscriber service HSS of the particularenabled device 20-23.

Embodiments of these teachings provide the technical effect of enablingan enhanced energy savings for the enabled devices 20-23, as well asenabling an efficient multichannel operation by the enabling device 24.Additionally, the enabled devices 20-23 are able to use the availablechannels indicated by the enabling device 24 without constantlymonitoring their own enablement on a specific channel

FIG. 5 is a logic flow diagram which describes an exemplary embodimentof the invention from the perspective of the enabling device 24. FIG. 5represents results from executing a computer program or an implementingalgorithm stored in the local memory of the enabling device 24, as wellas illustrating the operation of a method and a specific manner in whichthe enabling device 24 (or one or more components thereof) areconfigured to cause that overall host electronic device to operate.

Blocks 502 and 504 concern distributing the available channel lists andthe CVS interval, respectively. At block 502 a device is enabled foroperation in a license-exempt radio spectrum/band by providing to it alist of available license exempt radio channels. Block 503 shows thatthe device is also provided a parameter indicating an interval at whichcontact verification signals are to be sent, in which the contactverification signals verify whether the list provided at block 502remains valid. At block 504, there is repeatedly sent contactverification signals spaced in time from one another according to theinterval of block 503.

Further portions of FIG. 5 are directed to certain of the abovenon-limiting embodiments and implementations. Block 506 tells that theparameter comprises an explicit indication of a number of seconds or anumber of beacons between consecutive ones of the repeated contactverification signals. In the examples above there are a plurality ofsuch enabled devices, and as stated at block 508, such an explicitindication may be broadcast to the enabled device in any of a beaconmessage, a management frame, or system information.

Block 510 tells an alternative embodiment in which the parametercomprises an identifier of at least one of: the enabled device, theenabling device which is performing the elements of FIG. 5, and afrequency channel. In this case the CVS interval is derived from one ormore of those identifiers.

Remaining blocks of FIG. 5 relate to encryption. At block 512 thecontact verification signals are sent in encrypted broadcast messages,or in encrypted unicast messages directed to each of a plurality ofenabled devices individually. At least for the unicast messageembodiment, the list of block 502 which is provided to each of aplurality of enabled devices is a device-specific list (though not allsuch lists are necessarily different; some two or more devices may beenabled using the same channel list). At block 514 each encryptedbroadcast or unicast message which has the contact verification signalfurther comprises a new encryption key anytime a next consecutivebroadcast or unicast message which also has the contact verificationsignal uses different encryption. And finally at block 516, thedifferent encryption is decrypted by a combination of the new encryptionkey and an old encryption key.

FIG. 6 is a logic flow diagram which describes an exemplary embodimentof the invention from the perspective of one of the enabled devices20-23. FIG. 6 represents results from executing a computer program or animplementing algorithm stored in the local memory of one of the enableddevices 20-23, as well as illustrating the operation of a method and aspecific manner in which the enabled device 20-23 (or one or morecomponents thereof) are configured to cause that overall host electronicdevice to operate.

Blocks 602 and 604 concern the enabled device (which may or may not beenabled prior to block 602 depending on whether it had a previous list)obtaining its available channel lists and the CVS interval,respectively. At block 602 it receives from an enabling device a list ofavailable license exempt radio channels; and at block 604 it determinesan interval, from a parameter received from the enabling device, atwhich contact verification signals are spaced in time from one another.The contact verification signals verify whether the list received atblock 602 remains valid.

Further portions of FIG. 6 are directed to certain of the abovenon-limiting embodiments and implementations. Block 606 tells that theparameter comprises an explicit indication of a number of seconds or anumber of beacons between consecutive ones of the contact verificationsignals. Block 608 specifies that the explicit indication is receivedfrom the enabling device in one of a beacon message, a management frame,or system information.

Block 610 tells an alternative embodiment in which the parametercomprises an identifier of the enabled device which is performing FIG.6, the enabling device, and a frequency channel. In this case theinterval is derived from the said at least one identifier.

Remaining blocks of FIG. 6 relate to encryption. At block 612 theenabled device further receives the contact verification signals inencrypted broadcast messages, or in encrypted unicast messages directedto that enabled device. At block 614 each of the received encryptedbroadcast or unicast messages having the contact verification signalfurther comprises a new encryption key whenever a next consecutivebroadcast or unicast message having the contact verification signal usesdifferent encryption. Block 616 has the enabled device furtherdecrypting the next consecutive broadcast or unicast message using thedifferent encryption by combining the new encryption key and an oldencryption key.

The various blocks shown in FIGS. 5 and 6 may be considered as aplurality of coupled logic circuit elements constructed to carry out theassociated function(s), or specific result of strings of computerprogram code stored in a memory. Such blocks and the functions theyrepresent are non-limiting examples, and may be practiced in variouscomponents such as integrated circuit chips and modules, and that theexemplary embodiments of this invention may be realized in an apparatusthat is embodied as an integrated circuit. The integrated circuit, orcircuits, may comprise circuitry (as well as possibly firmware) forembodying at least one or more of a data processor or data processors, adigital signal processor or processors, baseband circuitry and radiofrequency circuitry that are configurable so as to operate in accordancewith the exemplary embodiments of this invention.

Reference is now made to FIG. 7 for illustrating a simplified blockdiagram of various electronic devices and apparatus that are suitablefor use in practicing the exemplary embodiments of this invention. InFIG. 7 an enabling device 24 is adapted for communication over awireless link (not specifically shown) with mobile apparatuses, such asmobile terminals, UEs or user devices which may implement the variousenabled devices 20, 21, 22. The enabling device 24 may be embodied as amacro eNodeB (a base station of an E-UTRAN system), a WLAN access point,a femto eNodeB, or other type of base stations or access points adaptedto provide the license-exempt channel lists and CVSs as detailed above.

In one particular implementation, any of the enabled devices 20, 21, 22may be embodied as a WLAN station STA, either an access point station ora non-access point station. In the case of an access point station, itwould function for TVWS and CVS purposes as a dependent/Mode I stationenabled by a Mode II device/enabling station 24 and for WLAN purposes asa WLAN access point for any non-access point STAs associated with itunder WLAN procedures. In such an embodiment the enabled access pointstation would not be able to enable any of those associated non-accesspoint STAs for TVWS purposes since it would not be operating as a ModeII or fixed device; for TVWS purposes it is operating only as a Mode Idevice that is enabled by a different Mode II device 24. But in thiscase the enabled access point station may still be able to advertise toits associated STAs and any other devices that are in radio range theidentifier of its enabling station 24.

The first enabled device 20 includes processing means such as at leastone data processor (DP) 20A, storing means such as at least onecomputer-readable memory (MEM) 20B storing at least one computer program(PROG) 20C, and also communicating means such as a transmitter TX 20Dand a receiver RX 20E for bidirectional wireless communications with theenabling device 24 via one or more antennas 20F. The RX 20E and the TX20D are each shown as being embodied with a modem 20H in aradio-frequency front end chip, which is one non-limiting embodiment;the modem 20H may be a physically separate but electrically coupledcomponent. The first enabled device 20 also has stored in the MEM 20B atblock 20G computer program code for determining the CVS interval fromthe parameter according to the various embodiments and implementationsabove.

The second enabled device 21 similarly includes processing means such asat least one data processor (DP) 21A, storing means such as at least onecomputer-readable memory (MEM) 21B storing at least one computer program(PROG) 21C, and communicating means such as a transmitter TX 21D and areceiver RX 21E and a modem 21H for bidirectional wirelesscommunications with the first enabled device 20 as well as the otherapparatus of FIG. 7 via one or more antennas 21F. The second enableddevice stores in its local MEM 21B at block 21G computer program codefor determining the CVS interval from the parameter similar to the firstenabled device 20.

Similarly, the third enabled device 22 includes processing means such asat least one data processor (DP) 22A, storing means such as at least onecomputer-readable memory (MEM) 22B storing at least one computer program(PROG) 22C, and communicating means such as a modem 22H forbidirectional communication with the other devices of FIG. 7. The thirdenabled device 22 also has stored in its local MEM 22B at block 22G thecomputer program code for determining the CVS interval from theparameter.

The enabling device 24 also includes its own processing means such as atleast one data processor (DP) 24A, storing means such as at least onecomputer-readable memory (MEM) 24B storing at least one computer program(PROG) 24C, and communicating means such as a transmitter TX 24D and areceiver RX 24E and a modem 24H for bidirectional wirelesscommunications with enabled devices 20, 21, 22 detailed above via itsantennas 24F. The enabling device 24 stores at block 24G in its localMEM 24B the parameter or parameters for determining the CVS interval,which it provides to the enabled devices 20, 21, 22 associated to it.

At least one of the PROGs 20C, 21C, 22C, 24C in the respective device20, 21, 22, 24 is assumed to include program instructions that, whenexecuted by the associated DP 20A, 21A, 22A, 24A, enable the device tooperate in accordance with the exemplary embodiments of this invention,as detailed above. Blocks 20G, 21G, 22G and 24G summarize differentresults from executing different tangibly stored software to implementcertain aspects of these teachings. In these regards the exemplaryembodiments of this invention may be implemented at least in part bycomputer software stored on the MEM 20B, 21B, 22B, 24B which isexecutable by the DP 20A, 21A, 22A, 24A of the various enabling andenabled devices, or by hardware, or by a combination of tangibly storedsoftware and hardware (and tangibly stored firmware). Electronic devicesimplementing these aspects of the invention need not be the entiredevices as depicted at FIG. 7, but exemplary embodiments may beimplemented by one or more components of same such as the abovedescribed tangibly stored software, hardware, firmware and DP, or asystem on a chip SOC or an application specific integrated circuit ASIC.

Various embodiments of the computer readable MEMs 20B, 21B, 22B and 24Binclude any data storage technology type which is suitable to the localtechnical environment, including but not limited to semiconductor basedmemory devices, magnetic memory devices and systems, optical memorydevices and systems, fixed memory, removable memory, disc memory, flashmemory, DRAM, SRAM, EEPROM and the like. Various embodiments of the DPs20A, 21A, 22A and 24A include but are not limited to general purposecomputers, special purpose computers, microprocessors, digital signalprocessors (DSPs) and multi-core processors.

Further, some of the various features of the above non-limitingembodiments may be used to advantage without the corresponding use ofother described features. The foregoing description should therefore beconsidered as merely illustrative of the principles, teachings andexemplary embodiments of this invention, and not in limitation thereof.

What is claimed is:
 1. An apparatus, comprising: at least one processor;and at least one memory storing a computer program; in which the atleast one memory with the computer program is configured with the atleast one processor to cause the apparatus to at least: enable a devicefor operation in a license exempt spectrum by providing to the device alist of available license exempt radio channels; provide to the device aparameter indicating an interval at which contact verification signalsare to be sent, in which the contact verification signals verify whetherthe list remains valid; and repeatedly send the contact verificationsignals spaced in time from one another according to the interval. 2.The apparatus according to claim 1, in which the parameter comprises anexplicit indication of a number of seconds or a number of beaconsbetween consecutive ones of the repeated contact verification signals.3. The apparatus according to claim 2, in which there are a plurality ofenabled devices for which the apparatus is configured to provide eachwith a device-specific list of available license exempt radio channels,the interval is the same for each of the plurality of devices, and theexplicit indication is broadcast to each of the plurality of enableddevices in one of: a beacon message, a management frame, or systeminformation.
 4. The apparatus according to claim 1, in which there are aplurality of enabled devices for which the apparatus is configured toprovide each with a device-specific list of available license exemptradio channels, the parameter is provided to each of the plurality ofenabled devices via unicast messages, and the interval is notnecessarily the same for each of the plurality of devices.
 5. Theapparatus according to claim 1, in which the parameter comprises anidentifier of at least one of: the device, an enabling device, and afrequency channel; and in which the interval is derived from the said atleast one identifier.
 6. The apparatus according to claim 1, in whichthe contact verification signals are sent in encrypted broadcastmessages, or in encrypted unicast messages.
 7. The apparatus accordingto claim 6, in which each encrypted broadcast or unicast message havingthe contact verification signal further comprises a new encryption keywhen a next consecutive broadcast or unicast message having the contactverification signal uses different encryption.
 8. The apparatusaccording to claim 7, in which the different encryption is decrypted bya combination of the new encryption key and an old encryption key. 9.The apparatus according to claim 1, in which the apparatus comprises afixed or a Mode II enabling device and the said device is a Mode Ienabled device.
 10. A method, comprising: enabling a device foroperation in a license exempt spectrum by providing to the device a listof available license exempt radio channels; providing to the device aparameter indicating an interval at which contact verification signalsare to be sent, in which the contact verification signals verify whetherthe list remains valid; and repeatedly sending contact verificationsignals spaced in time from one another according to the interval. 11.The method according to claim 10, in which the parameter comprises anexplicit indication of a number of seconds or a number of beaconsbetween consecutive ones of the repeated contact verification signals.12. The method according to claim 11, in which there are a plurality ofenabled devices each of which is provided with a device-specific list ofavailable license exempt radio channels, the interval is the same foreach of the plurality of devices, and the explicit indication isbroadcast to the devices in one of: a beacon message, a managementframe, or system information.
 13. The method according to claim 10, inwhich there are a plurality of enabled devices each of which is providedwith a device-specific list of available license exempt radio channels,the parameter is provided to each of the plurality of enabled devicesvia unicast messages, and the interval is not necessarily the same foreach of the plurality of devices.
 14. The method according to claim 10,in which the parameter comprises an identifier of at least one of: thedevice, an enabling device, and a frequency channel; and in which theinterval is derived from the said at least one identifier.
 15. Themethod according to claim 10, in which the contact verification signalsare sent in encrypted broadcast messages, or in encrypted unicastmessages.
 16. The method according to claim 15, in which each encryptedbroadcast or unicast message having the contact verification signalfurther comprises a new encryption key when a next consecutive broadcastor unicast message having the contact verification signal uses differentencryption.
 17. A non-transitory computer readable memory storing acomputer program comprising: code for enabling a device for operation ina license exempt spectrum by providing to the device a list of availablelicense exempt radio channels; code for providing to the device aparameter indicating an interval at which contact verification signalsare to be sent, in which the contact verification signals verify whetherthe list remains valid; and code for repeatedly sending contactverification signals spaced in time from one another according to theinterval.
 18. The non-transitory computer readable memory according toclaim 17, in which the parameter comprises an explicit indication of anumber of seconds or a number of beacons between consecutive ones of therepeated contact verification signals.
 19. The non-transitory computerreadable memory according to claim 17, in which the parameter comprisesan identifier of at least one of: the device, an enabling device, and afrequency channel; and in which the interval is derived from the said atleast one identifier.
 20. The non-transitory computer readable memoryaccording to claim 17, in which the contact verification signals aresent in encrypted broadcast messages, or in encrypted unicast messages.